This invention relates to a signature panel to be formed on the surface of cards such as debit cards, credit cards, identification cards and membership cards. The invention also relates to a process for producing such a signature panel.
Debit cards, credit cards, identification cards, membership cards and other cards must be checked for the legitimacy of not only themselves but also their holders. A method of meeting this requirement is to have cardholders sign their names in an area specified as a "signature panel" which is indicated by 12 and which is provided in substantially the center of the card 10 as shown in FIG. 1.
A major problem with cards is that a person who is not the true holder of a card can use it if he tampers the authentic signature of the true card holder.
Various methods have been proposed to prevent the forgery and tampering of cards. One method is using a signature panel that is provided on the surface of a synthetic resin board and which has formed on the writing surface a graphic pattern that will change upon exposure to alcohols, solvents, bleaching agents and surfactants. Several versions of such signature panels have been proposed by American Banknote Co., Ltd., U.S.A., Maccorquodale Co., Ltd., U.S.A., Thomas de larue Co., Ltd., U.S.A., Harrison & Sons, Ltd., U.K., etc. The writing surfaces of the signature panels proposed by those companies are provided with graphic patterns that will change upon exposure to alcohols, solvents (e.g. methyl ethyl ketone, toluene, gasoline and thinners), bleaching agents or surfactants (e.g. detergents) (which are hereunder collectively referred to as "chemicals"). If someone wants to tamper the signature inscribed on such panels, he has to erase it by a certain means and thereafter write a false signature. However, if the authentic signature is erased with chemicals, the graphic pattern provided in the signature panel will simultaneously undergo some change such as dissolution, swelling, fading or change of color, which all make the act of tampering clearly evident.
The signature panels described above have to be bonded to the card substrate. If the card substrate is made of polyvinyl chloride without any surface treatment, there is no need to use solvent-containing adhesives and the signature panels can be bonded to the card substrate merely by thermocompression which is conducted at a fairly high temperature of ca. 150.degree. C. However, if the card substrate has a polyvinyl chloride oversheet coated on the entire surface, accompanied by the formation of a colored graphic pattern (a card using this substrate is often referred to as an "overprint card"), the graphic pattern will deform thermally at elevated temperatures of 150.degree. C. and the signature panel cannot be bonded to the substrate without using an adhesive.
Needless to say, the conventional signature panels cannot be thermocompressed onto card substrates such as polyethylene terephthalate (PET) sheets, metal sheets and glass sheets and an adhesive must be used to bond them together.
However, if an adhesive is applied in order to bond the signature panels to various types of card substrates, the solvents contained in the adhesive will cause a change in the printed graphic pattern on the writing surface of the panels which will change upon exposure to chemicals and this has made it practically impossible to use adhesives for the purpose of bonding signature panels and card substrates.